A stent is a type of endoluminal prosthesis. Stents are generally tubular open-ended structures providing support for damaged, collapsing, or occluded blood vessels. They are radially expandable from a radially compressed configuration for delivery to the affected vessel site to a radially expanded configuration when deployed at the affected vessel treatment site, with the radially expanded configuration having a larger diameter than the radially compressed configuration. Stents are flexible, which allows them to be inserted through, and conform to, tortuous pathways in the blood vessels. Stents are generally inserted in the radially compressed configuration and expanded to the radially expanded configuration either through a self-expanding mechanism, or through the use of a balloon catheter.
A graft is another type of endoluminal prosthesis, which is used to repair and replace various body vessels. Whereas the stent provides structural support to hold a damaged vessel open, a graft provides an artificial lumen through which blood may flow. Grafts are tubular devices that may be formed of a variety of materials including textile, and non-textile materials.
Stents and graft may be combined to form a stent-graft prosthesis, providing both structural support and an artificial lumen through which blood may flow. A stent-graft prosthesis is particularly useful to isolate aneurysms or other blood vessel abnormalities from normal blood pressure, reducing pressure on the weakened vessel wall, thereby reducing the chance of vessel rupture while maintaining blood flow. A stent-graft prosthesis is placed within the aneurysmal blood vessel to create a new flow path and an artificial flow conduit through the aneurysm, thereby reducing the exertion of blood pressure on the aneurysm. The stent-graft prosthesis incorporates one or more radially expandable stent(s) to be radially expanded in situ to anchor the tubular graft to the wall of the blood vessel at sites upstream and downstream of the aneurysm. Thus, endovascular stent-graft prostheses are typically held in place by mechanical engagement and friction by the outward radial force imparted on the wall of the blood vessel by the self-expanding or balloon expandable stent(s).
The design of a stent-graft prosthesis must balance strength and flexibility. Generally, increasing the strength a stent-graft prosthesis reduces its flexibility. Conversely, increasing the flexibility of stent-graft prosthesis generally decreases its strength. For example, a stent-graft prosthesis formed with a single helical wire is generally highly flexible but the single helical wire generally provides little support or strength when the stent-graft prosthesis is under compression. More particularly, the single helical wire has the potential to collapse under local compression that may be caused by plaque in peripheral vessels or caused by other prostheses in aortic parallel or chimney applications. Damage or malfunctioning of any portion of the single helical wire along the length of the stent-graft prosthesis cause the entirety of the stent-graft prosthesis to fail, as there are no failsafe or backup support structures on a stent-graft prosthesis formed by a single helical wire.
Accordingly, there is a need for an improved stent-graft prosthesis having additional strength and redundant structure while maintaining flexibility.